Conventional beamforming systems are often cumbersome to manufacture. In particular, conventional beamforming antenna arrays require complicated feed structures and phase-shifters that are impractical to be implemented in a semiconductor-based design due to its cost, power consumption and deficiency in electrical characteristics such as insertion loss and quantization noise levels. In addition, such beamforming arrays make digital signal processing techniques cumbersome as the operating frequency is increased. In addition, at the higher data rates enabled by high frequency operation, multipath fading and cross-interference becomes a serious issue. Adaptive beamforming techniques are known to combat these problems. But adaptive beamforming for transmission at 10 GHz or higher frequencies requires massively parallel utilization of A/D and D/A converters.
To provide a beamforming system compatible with semiconductor processes, the applicant has provided a number of integrated antenna architectures. For example, U.S. application Ser. No. 11/454,915, the contents of which are incorporated by reference, discloses a beamforming system in which an RF signal is distributed through a transmission network to integrated antenna circuits that include a beamforming circuit that adjusts the phase and/or the amplitude of distributed RF signal responsive to control from a controller/phase manager circuit. In a receive configuration, each beamforming circuit adjusts the phase and/or the amplitude of a received RF signal from the corresponding integrated circuit's antenna and provide the resulting adjusted received RF signal to the transmission network. Although such integrated antenna circuits consume a relatively small amount of power, transmission loss is incurred through the resulting RF propagation in the transmission network. To account for such loss, U.S. application Ser. No. 11/454,915 discloses a distributed amplification system such that RF signals propagated through the transmission network are actually amplified rather than attenuated. However, the transmission network introduces dispersion as well.
To avoid the dispersion introduced by an RF transmission network, an alternative integrated circuit (which may also be denoted as an integrated oscillator circuit) has been developed such as disclosed in U.S. Pat. No. 6,982,670. For example, each integrated oscillator/antenna circuit may include an oscillator such as a phase-locked loop (PLL) and a corresponding antenna and mixer. In such an embodiment, each PLL is operable to receive a reference signal and provide a frequency-shifted signal output signal that is synchronous with the reference signal. Should an integrated oscillator/antenna circuit be configured for transmission, its output signal is upconverted in the unit's mixer and the upconverted signal transmitted by the corresponding antenna. Alternatively, should an integrated oscillator/antenna circuit be configured for reception, a received RF signal from the unit's antenna is downconverted in the mixer responsive to the frequency-shifted output signal from the PLL. Although the integrated oscillator circuit approach does not have the dispersion issues resulting from propagation through a transmission network, the inclusion of an oscillator in each integrated oscillator circuit demands significantly more power than the transmission network approach.
To avoid the dispersion resulting from propagation through a transmission network or the expense of an integrated oscillator approach, a distributed oscillator architecture has been developed as disclosed in U.S. application Ser. No. 11/536,625. In this architecture, a resonant transmission network with distributed amplification is driven by a triggering pulse waveform such that the entire transmission network oscillates acting as a distributed oscillator. In this fashion, high frequency RF signals and/or narrowband pulses from the resonant transmission signal are coupled a globally synchronized fashion to the various integrated antennas. Each antenna (or a subset of antennas) may include a phase-shifter and/or attenuator to provide beamforming capabilities. Although this resonant approach is compatible with conventional semiconductor processes, the smaller dimensions of modern semiconductor processes are not compatible with large voltages. For example, it is conventional in certain CMOS processes to limit signal voltages to 2.5 V or even 1.5V or less. Voltages in excess of these limits may damage the devices or cause long-term reliability issues adversely impacting their performance. This limit on voltage places a limit on the amount of transmit power that can be delivered to the antennas. In addition, it may be desirable that the resonant oscillation amplitude over the resonant transmission network be maximized. Accordingly, there is a need in the art for integrated solutions compatible with high power operation. Moreover, there is a need in the art for a resonant transmission network that has an enhanced oscillation amplitude.